In general, a reticle or mask is a lithographic tool which contains a pattern that is transferred to a wafer. In the field of integrated circuits, a reticle can be classified as a plate that contains the pattern for one or more die but is not large enough to transfer a wafer sized pattern all at once. In the field of integrated circuits, a mask can be classified as a plate that contains a pattern large enough to pattern a whole wafer at a time. The pattern for reticles and masks can be formed of opaque and non-opaque areas disposed on a glass plate (e.g., fused silica, soda-lime glass, borosilicate glass, fluorinated silicone dioxide, and quartz). The opaque areas often include chromium, emulsion, ion oxide, and/or chromium oxide. Alternatively, the pattern can be manifested on a conventional phase shift mask. Conventional phase shift masks can include opaque areas and phase shift areas which define the pattern.
Semiconductor fabrication techniques often utilize a mask or reticle. Radiation is provided through or reflected off the mask or reticle to form an image on a semiconductor wafer. The wafer is positioned to receive the radiation transmitted through or reflected off the mask or reticle. The image on the semiconductor wafer corresponds to the pattern on the mask or reticle. The radiation can be light, such as ultraviolet light, vacuum ultraviolet light, etc. The radiation can also be x-ray radiation, e-beam radiation, etc.
Generally, the image is focused on the wafer to pattern a layer of material, such as, photoresist material. The photoresist material can be utilized to define doping regions, deposition regions, etching regions, or other structures associated with an integrated circuit (IC). The photoresist material can also define conductive lines or conductive pads associated with metal layers of an integrated circuit. Further, the photoresist material can define isolation regions, transistor gates, or other transistor structures and elements.
A conventional lithographic system is generally utilized to project the image to the wafer. For example, the conventional lithographic system includes a source of radiation, an optical system, and a reticle or photomask. The source of radiation provides radiation through the optical system and through or off of the mask or reticle.
The pattern image on the reticle is stepped and repeated to expose an entire substrate, such as, a wafer, while the pattern on a photomask or mask is transmitted to an entire wafer. However, as used in this application, the terms reticle, photomask, and mask are interchangeable unless specifically described otherwise. The photomask can be positive or negative (clear-field or dark-field tools).
According to a conventional mask patterning process, the glass substrate is polished in a multiple step process. The polished substrate is cleaned and inspected for defects. After inspecting the glass substrates, the glass substrates are coated with an opaque material, (e.g., an absorbing layer). The glass substrates can be coated in a sputter deposition process.
The opaque material is selectively etched according to a lithographic process. The opaque material is coated with a resist material. The resist material is patterned via an optical pattern generator. A conventional optical pattern generator utilizes shutters, light sources, optical components, and movable stages to produce the appropriate optical pattern on the resist material. The resist material is then removed in accordance with the optical pattern. The opaque material is removed in accordance with the remaining resist material. The opaque material can be removed by wet etching. Thus, the absorbing material is patterned or etched in accordance with the image desired to be formed on the substrate (e.g., the image provided by the optical pattern generators).
Manufacturing masks and reticles is time consuming and costly. Further, the equipment including the optical pattern generators required to manufacture the masks and reticles is expensive. Masks and reticles must be manufactured for each image to be transferred on the wafer.
In general, phase shift masks include phase shifting areas surrounding mask features. These phase shifting areas alter the phase of light passing through to improve resolution depth of focus for the mask features. Alternating phase shift masks use alternating apertures etched in quartz on the mask to affect the phase shift. Attenuating phase shift masks use a partially opaque phase shifting absorber (referred to as the attenuator) material, such as, MoSi. Only a percentage of light passes through the opaque material and the phase of the light can be changed by 180 degrees.
Two attenuator properties can be optimized with attenuated phase shift masks: thickness and transparency. Thickness of a phase shifting material can be adjusted to obtain the appropriate phase. Transparency of the phase shifting material can be adjusted to determine how much phase delayed light passes through
Traditionally, refractory metal oxides and silicides have been used for phase shift and transparency in attenuated phase shift masks (PSM). For example, molybdenum silicon (MoSi) and chromium oxide (CrO2) can be used. Optimal mask performance can be difficult to achieve with such materials. Some of the difficulties encountered with these materials are etchability and reflection control for mask patterning. Typically, the etch selectives of the photoresist is poor to these materials. The amorphous carbon is designed to transfer a photoresist pattern with high selectivity.
It would be desirable to use amorphous carbon as a partially transmissive phase shifting film for attenuated phase shift mask (PSM) fabrication. Further, it would be desirable to use amorphous carbon in attenuators of a PSM. Yet further, it would be desirable to use the properties of amorphous carbon in a PSM. Yet further still, there is a need for an amorphous carbon-based PSM. Yet further, there is a need for a method of making an amorphous carbon-based PSM.